1. Field of the Art
The present invention relates generally to a rotary fluid machine of a Roots type having resin-coated rotors, and more particularly to a technique for improving displacement efficiency of such type of rotary fluid machines.
2. Related Art Statement
In a rotary fluid machine of a Roots type such as rotary lobe-type pump or air compressor or blower, two lobes or rotors supported for rotation in opposite directions are accommodated in a chamber formed in a hollow housing structure, such that there exist small clearances between the outer surfaces of the two rotors, and between the outer surfaces of the rotors and the inner surfaces of the housing structure. It is desired to keep these clearance to a minimum, for ensuring maximum displacement efficiency of the fluid machine.
Referring to FIG. 4, there are partly shown one of two rotors 10 and a housing structure of a known fluid machine of the type indicated above. The housing structure consists of three pieces, that is, a main housing body 14 which has a bore which is open at its opposite ends, and a pair of covering members 16, 16 which close the opposite open ends of the bore and which cooperate with the housing body 14 to define a chamber 12 in which. the rotors 10 are accommodated. In this arrangement, the blanks for the housing body 14 and the covering members 16, 16 may be readily machined or processed so that the inner surfaces of the covering members 16, 16 defining the opposite ends of the chamber 12 are at right angles to the inner peripheral surface of the housing body 14. Accordingly, a clearance "a" between the outer peripheral surface of each rotor 10 and the inner surface of the housing body 14, and a clearance "b" between the end faces of the rotor 10 and the inner surface of the covering members 16, may be made comparatively small.